Right-Click on MY Computer and select Properties. go to Advance Options-->Startup and Recovery. There should be an option there so the machine won't restart on a bluescreen. When the machine bluescreens, you will get an exception code (usually 0x0000something).
Go with that code to http://support.microsoft.com, and check it there.
Also, you can go to Control Panel-->Administrative Tools-->Event Viewer-->System Events (?) and scroll down to the time of the bluescreen. The exception code should be there too.